518 research outputs found
Optical and X-ray Properties of CAL 83: I. Quasi-periodic Optical and Supersoft Variability
We have studied the long-term (~ years) temporal variability of the prototype
supersoft X-ray source (SSS) CAL 83 in the LMC, using data from the MACHO and
OGLE projects. The CAL 83 light curve exhibits dramatic brightness changes of
~1 mag on timescales of ~450 days, and spends typically ~200 days in the
optical low state. Combined with archival XMM-Newton X-ray observations these
represent the most extensive X-ray/optical study to date of this system, and
reveal in much greater detail that the X-ray light curve is anti-correlated
with the optical behaviour. This is remarkably similar to the behaviour of the
"transient" SSS, RX J0513.9-6951, where the SSS outbursts recur on a timescale
of ~168 days, and also anti-correlate with the optical flux. We performed
simple blackbody fits to both high and low state X-ray spectra, and find that
the blackbody temperature and luminosity decrease when the optical counterpart
brightens. We interpret these long-term variations in terms of the limit-cycle
model of Hachisu & Kato (2003a), which provides further support for these
systems containing massive (~1.3 Msun) white dwarfs. In addition, we have
refined their orbital periods in the MACHO and OGLE-III light curves to values
of 1.047529(1) days and 0.762956(5) days for CAL 83 and RX J0513.9-6951,
respectively.Comment: 9 pages, 8 figures, 3 tables, accepted for publication in MNRA
Angiogenesis Meets Skeletogenesis: The Cross-Talk between Two Dynamic Systems
In this chapter, we describe the complex relationship between angiogenesis and skeletogenesis. While much is known about the interactions of these two dynamic systems for bones that ossify via a cartilage template, comparatively little is known about directly ossifying bones. Most of the bones of the head develop from osteogenic condensations and undergo intramembranous (direct) ossification during development. Our understanding of the relationship between osteogenic cell condensations (in particular) and angiogenesis is currently inadequate and prevents a comprehensive understanding of vertebrate head development. This chapter highlights our understanding of both direct and indirectly ossifying bones shedding light on where there are important gaps in our understanding
AE Aquarii: A Short Review
The nova-like variable AE Aquarii has been continuously studied since its discovery on photographic plates in 1934. In this short review the peculiar multi-wavelength properties of AE Aquarii will be reviewed and explained in context of its evolution from a high mass transfer phase, during which period it could have been a supersoft X-ray source (SSS)
Insights into the pathogenesis of viral haemorrhagic fever based on virus tropism and tissue lesions of natural Rift Valley fever
Rift Valley fever phlebovirus (RVFV) infects humans and a wide range of ungulates and historically has caused devastating epidemics in Africa and the Arabian Peninsula. Lesions of naturally infected cases of Rift Valley fever (RVF) have only been described in detail in sheep with a few reports concerning cattle and humans. The most frequently observed lesion in both ruminants and humans is randomly distributed necrosis, particularly in the liver. Lesions supportive of vascular endothelial injury are also present and include mild hydropericardium, hydrothorax and ascites; marked pulmonary congestion and oedema; lymph node congestion and oedema; and haemorrhages in many tissues. Although a complete understanding of RVF pathogenesis is still lacking, antigen-presenting cells in the skin are likely the early targets of the virus. Following suppression of type I IFN production and necrosis of dermal cells, RVFV spreads systemically, resulting in infection and necrosis of other cells in a variety of organs. Failure of both the innate and adaptive immune responses to control infection is exacerbated by apoptosis of lymphocytes. An excessive proinflammatory cytokine and chemokine response leads to microcirculatory dysfunction. Additionally, impairment of the coagulation system results in widespread haemorrhages. Fatal outcomes result from multiorgan failure, oedema in many organs (including the lungs and brain), hypotension, and circulatory shock. Here, we summarize current understanding of RVF cellular tropism as informed by lesions caused by natural infections. We specifically examine how extant knowledge informs current understanding regarding pathogenesis of the haemorrhagic fever form of RVF, identifying opportunities for future research
Optical observations of "hot" novae returning to quiescence
We have monitored the return to quiescence of novae previously observed in
outburst as supersoft X-ray sources, with optical photometry of the
intermediate polar (IP) V4743 Sgr and candidate IP V2491 Cyg, and optical
spectroscopy of these two and seven other systems. Our sample includes
classical and recurrent novae, short period (few hours), intermediate period
(1-2 days) and long period (symbiotic) binaries. The light curves of V4743 Sgr
and V2491 Cyg present clear periodic modulations. For V4743 Sgr, the modulation
occurs with the beat of the rotational and orbital periods. If the period
measured for V2491 Cyg is also the beat of these two periods, the orbital one
should be almost 17 hours. The recurrent nova T Pyx already shows fragmentation
of the nebular shell less than 3 years after the outburst. While this nova
still had strong [OIII] at this post-outburst epoch, these lines had already
faded after 3 to 7 years in all the others. We did not find any difference in
the ratio of equivalent widths of high ionization/excitation lines to that of
the Hbeta line in novae with short and long orbital period, indicating that
irradiation does not trigger high mass transfer rate from secondaries with
small orbital separation. An important difference between the spectra of RS Oph
and V3890 Sgr and those of many symbiotic persistent supersoft sources is the
absence of forbidden coronal lines. With the X-rays turn-off, we interpret this
as an indication that mass transfer in symbiotics recurrent novae is
intermittent.Comment: In press in Monthly Notices of the Royal Astronomical Societ
From “Smart in the Box” to “Smart in the City”: Rethinking the Socially Sustainable Smart City in Context
18 months embarg
Towards an agenda of place, local agency-based and inclusive smart urbanism
"The volume explores the question of what it means for a city to be 'smart', raises some of the tensions emerging in smart city developments, and considers the implications for future ways of inhabiting and understanding the urban condition ..
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